Process for preventing the dissolution of metals in pickling baths



flicked Mi; 19311 UNITED "STATES PATENT; OFFICE LORIN .B. SEER-ELL, OF AKRON, OHIO, ASSIGNOR TO THE GOODYEAR TIRE & YU'IBBER COMPANY, OF AKRON, OHIO, A CORPORATION OF OHIO PBOCES FOR PREVENTING THE DISSOLUTION OF METALS IN PICKLING BATES No Drawing.

it has particular relation to the preparation of a non-corrosive acid solution adapted to remove rust and other impurities from such articles without roughening or etching the surface thereof.

One object of the invention consists in the provision of a corrosion inhibiting agent for a solution of the character above-designated which is more eificientin its operation than the materials heretofore employed for that purpose.

Another object of the invention is to provide a corrosion inhibiting agent for pickling solutions that is composed of relatively inexpensive ingredients.

In the iron and steel industry it is customary to treat iron or steel objects with an acid pickling solution in order to remove rust and other impurities from the surface thereof prior to the application of various coating materials such as zinc, paints or lacquers. Most acids employed-for this purpose are more or less objectionable, because they not only react with the iron oxide or rust upon the articles but they attack and corrode the metals themselves, thus so roughening the surface thereof as to render it difficult to apply a smooth and uniform coating upon the exposed surfaces of the articles. The corrosion of the metal is also objectionable, because the interaction of the metal and the acid results in so weakening the solution that 111 a comparatively short time it becomes diluted to such an extent as to necessitate the addition of new acid or a replenishing of the entire solution. 7

' ance with while well adapted for the removal of oxldes and such impurities from the surfaces of the A pickling solution prepared in accordthe provisions of this invention iron or steel articles themselves, has but very slight corrosive effect u on the metal. It follows that the solution oes not waste away rapidly and, therefore, it can be used for a relatively long period of time without being replenished This invention consists inthe-discovery that compounds containing sulphur,

' Application filed October 21, 1927. Serial No. 227,859.

such as those obtained by theintcractim 9 eselp hi an th-alae nsles. w "i termlied W1 '32. pickling solution, very eatly reduce the corrosive effects of the acid in the solution upon the metal itself. The use ofaldehydes as negative catalysts or inhibitors of corrosion in pickling solutions is well known in the art and a complete disclosure thereof is contained in U. S. Patent No. 1,470,225.

The motion products of the aldehydes formaldehyde which fall within the scope of the invention: I

H, ns-t-sn H: H: 'gg-t-s-tA n I Hi} HI :"HT" fgs;j-s-tJ-s t-sn It will be observed'that the "compounds indicated in the above formulas are mercaptans. Under certain circumstances, however, the hydrogenatoms of the mercaptan groups are lost and the end sulphur atoms become linked together. The compounds in- 5 dicated by the following structural formulas are examples of the latter materials:

i if

These materials. are well known in chemical literature andni'e' discussed particularly in Berichte, ,Vol f II 1870.

The following method be employed with satisfactory results tain materials with hydrogen sulphide are relatively disforthe year 1890, page of this class. A forty percent solution of formaldehyde is cooled to a temperature ranging from 0 to 10 C. and hydrogen sulphide is then bubbled therethrough until the solution has increased approximately twenty-five percent in weight. The hydrogen sulphide saturated solution is filtered in order to remove any slight precipitate that may form and is then diluted with an equal volume of water. The solution itself may be introduced into an acid pickling solution and employed as a corrosion inhibitor or negative catalyst. If it is permitted to stand for a period between ten and twelve hours it sets into a relatively stiff paste or putty-like material which may be dissolved in the pickling solution and employed as a corrosion inhibitor with excellent results.

In order to obtain the putty-like material it is essential that the aldehyde solution be treated with hydrogen sulfide until about twenty-five percent by weight of the gas has been absorbed; It is possible, however, to stop the treatment before that stage of saturation has been reached and still obtain a very satisfactory corrosion inhibitor, although it will be in the liquid state. It is probable that from one to twenty-five percent by weight of hydrogen sulfide should be present in order to obtain the best results from the inhibitor. It is to be understood, however, that the invention is not limited to these specific proportions.

The compound formed by this method appears to be a mixture of materials having the following structural formulae:

The material represented by the formula:

H: s S

(tri-thio aldehyde) may be prepared by permitting the reaction product of the formaldehyde and hydrogen sulphide to stand a few hours until it becomes cloudy. At this time a quantity of material will be deposited upon the bottom of the flask. The liquid portion is then filtered and is treated with half its volume of acid, such as hydrochloric acid, and is heated to the boiling point. It then becomes clear and upon being allowed to cool the tri-thio formaldehyde is deposited as a crfystalline material having a melting point 0 about 218 C.

Hydrogen sulphide will also react with other aldehydes than formaldehyde to form valuable corrosion inhibitors. The reaction products of hydrogen sulphide with butyl aldehyde and with a-ldol are excellent materials for this purpose. Butyl aldehyde will absorb approximately seventeen percent of hydrogen sulphide while aldol absorbs approximately twelve percent. The invention is not limited to those particular percents, however.

Aldehydes will also react with other suli est an ogen sulphide foi example .with sod1un 1 or potassinnisulphide, to form products which are good inhibitors.

The elficiency of the materials prepared in accordance with the procedure outlined is illustrated by the following tables the data for which was obtained by permitting portions of 300 cc. each of a ten percent solution of sulphuric acid containing the requisite amount of inhibitor to react upon various iron or steel articles.

Table I Per cent additional loss upon Per cent allowinr: wt. loss articles to 15 mins. remain in bath 30 mins. longer Control (H1804 without inhibitor) 5. 29 4. 9O .3 cc. liquid HOBO-His product 1.18 .05 .6 cc. 40% ECHO straight 1.02 23 5 gm. solid tri-thio formaldehyde 1. 10 04 Table II Per cent additional loss upon Per cent allowing wt. loss articles to 15 mins. remain in bath 30 mins. longer Control 2. 14 13. 17 Butyl aldehyde-Hi8 1.- 13 .18 AldOl-HzS 1. 07 18 The paste obtained by allowing the formaldehyde hydrogen sulphide reaction product to stand for a few hours is also an excellent corrosion inhibitor, as indicated by the 1 table appearing below.

10% H=SO.Inhibitor 1 pt. to 1000 acid It will be observed from the first of the tables that the reaction product of formaldehyde and hydrogen sulphide consisting principally ofthe compounds having the following formulas:

H: ns-c-sn Methylene mercaptan H: H: ns-t-s-t-sa Thio-di-methylcne mercaptan H1 H: H: HS-(J-S- S-(J-SH Dithio-tri-methylene mercaman c-s t d-s Dimethylenc tri sulphide even in the proportions of .3 cc. for 300 cc. of acid, is a more efficient corrosion inhibitor, particularly for relatively long periods, than a pickling solution of the same concentration containing as much as .6 cc. of formaldehyde.

Although I have described in detail only the preferred embodiments of the invention, it will be apparent to those skilled in the art that it is not so limited but that various minor modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

What I claim is:

1. A bath for pickling metals containing a. non-oxidizing mineral acid and a reaction product of an aldehyde and hydrogen sulphide.

2. A pickling bath for.iron or steel articles containing a non-oxidizing mineral acid and a reaction product of an aldehyde and a soluble inorganic sulphide.

3. A pickling bath for iron or steel containing a non-oxidizing mineral acid and a material having the following formula: HS-RSH, in which R is a hydrocarbon group. a

4. A pickling bath for iron or steel articles containing a nonoxidizing mineral and material having the following formula: HS-RSH, in which R is a sulphur substituted hydrocarbon group.

5. A pickling bath for iron or steel articles containing a reaction product of hydrogen sulphide and formaldehyde.

6. A pickling bath for iron or steel containin a reaction product of formaldehyde with rom 1 to 25% by weight of hydrogen sulphide.

7. A pickling bath for iron or steel which contains tri-thio-formaldehyde. 0

bath for iron containing bodies consisting of a solution of sulphuric acid containing a reaction product of an aldehyde and a soluble inorganic sulfide.

9. A pickling bath for iron containing bodies consisting of a solution of sulphuric acid containing a reaction product of an aldehyde and hydrogen sulfide.

A pickling bath for iron containing bodies consisting of a solution of sulphuric acid containing a reaction product of formaldehyde and a soluble inorganic sulfide.

11. A pickling bath for iron containing bodies consisting of a solution of sulphuric acid containing a reaction product of a straight chain aldehyde and a soluble inorganic sulfide.

12. A pickling bath for iron containing bodies consisting of a solution of sulphuric acid containing a reaction product of formaldehyde and hydrogen sulfide.

13. A pickling bath for iron containing bodies consisting of a solution of sulphuric acid containing a reaction product of a git-aight chain aldehyde and hydrogen sul- 14. A pickling bath for iron and steel articles containing a non-oxidizing mineral acid and a material having the following structural formula: HSR-SH, in which the group R comprises alternating carbon and sulphur atoms.

15. A metal treating compound comprising a non-oxidizing acid solution containing from 0.05 to 1% of a sulphur containing aldehyde compound.

16. A metal treating compound comprising a non-oxidizing acid solution containing from 0.05 to 1% of a tri-thio-aldehyde.

17. The process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a solution containing a sulphurized aldehyde compound dissolved in a non-oxidizing acid.

18. The process of pickling iron and steel roducts which comprises subjecting the metal to be pickled to the action of a solution containing a thio aldehyde derivative dissolved in a non-oxidizing acid.

In witness whereof, I have hereunto signed my name.

Si ed at Akron, in the county of Summit, and tate of Ohio, this 20th day of October,

LORIN B. SEBRELL. 

